The present application is related to U.S. Ser. No. 09/191,133, filed Nov. 13, 1998 and entitled xe2x80x9cSubnetwork Layer For A Multimedia Mobile Network;xe2x80x9d and U.S. Ser. No. 09/191,132, filed Nov. 13, 1998 and entitled xe2x80x9cAddressing Scheme For A Multimedia Mobile Network.xe2x80x9d
1. Field of the Invention
The present invention relates to mobile communications systems and, more particularly, to mobility management techniques in such systems that may include multimedia applications in a highly dynamic networking environment.
2. Background of the Invention
Several important mobility management issues need to be addressed in designing a communications system wherein the system is characterized by a dynamic network topology (e.g., mobile system access points or network nodes) and a relatively large number of mobile end users. Particularly, critical among them are issues such as: keeping track of mobile end users and access point locations in the system (i.e., location management); reaching and initiating communications with a mobile end user (i.e., mobile access); and continuity of service when a mobile end user moves between coverage areas associated with system access points (i.e., handoff management). Existing networks do provide solutions to these problems in their specific domains. As prior art, we discuss the solutions provided by Cellular Digital Packet Data (CDPD) networks, Cellular/Personal Communications Services (Cellular/PCS) systems, and Mobile Internet Protocol (mobile IP) networks.
CDPD networks consist of Mobile Data Intermediate Systems (MDISs), Mobile Data Base Stations (MDBSs), Mobile End Stations (MESs). An MDBS offering CDPD services helps a roaming MES register with the MDIS (called the serving MDIS) with which the MDBS is associated by acting as a conduit for the registration message. The serving MDIS informs the home MDIS of the MES of the latter""s presence in its coverage area. When a host needs to send data to an MES, it does not have to be aware of the mobility aspect of the MES, it simply transmits data using the MES""s IP address as the destination address. The IP packets are terminated at the home MDIS which encapsulates them in new data packets using the serving MDIS address as the destination address. The encapsulated data packets for the MES are forwarded to the serving MDIS of the MES. At the serving MDIS, packets are de-capsulated to reveal the MES""s address. The serving MDIS sends the original data packets to the right channel where the MES is currently located. The MES receives the data packets. If the MES needs to reply, it directly sends data packets using the remote host""s IP address as the destination address.
Intra-MDIS (i.e., between the two MDBSs served by the same MDIS) handoffs in CDPD are quick and simple because the data link between the MDIS and the mobile remains intact. However, Inter-MDIS handoffs could interrupt service since the data link will most likely be torn down when a mobile moves between MDISs. In this case, users have to reregister with the new serving MDIS. CDPD systems are further described in K. Budka et al., xe2x80x9cCellular Digital Packet Data Networks,xe2x80x9d Bell Labs Technical Journal, Vol. 2, No. 3 (Summer 1997); xe2x80x9cCellular Digital Packet Data Systems Specification: Release 1.1, xe2x80x9d CDPD Forum, Inc., Chicago (1995); and M. S. Taylor et al., xe2x80x9cInternetwork Mobility: The CDPD Approach,xe2x80x9d Prentice Hall PTR, Upper Saddle River, N.J. (1996).
In Cellular/PCS systems, Home Location Registers (HLRs) and Visitor Location Registers (VLRs) are used to handle mobility management. HLRs and VLRs potentially can reside anywhere in the network. An HLR contains profile information about each of its mobile subscribers and the address of the current VLRs of its mobiles. Each Mobile Switching Center (MSC) has a VLR which tracks all mobiles currently receiving service in the serving MSC""s coverage area. Whenever a mobile enters an area served by a new VLR and registers itself there, the latter informs the mobile""s HLR of the change in the mobile""s location. In addition, the VLR downloads the service profile of the roaming mobile as well as other information necessary for call termination at the mobile.
When a mobile terminated call is initiated, the first PSTN switch encountered by the calling party realizes that the called party number is a cellular/PCS number, thus it queries its HLR for the mobile""s location. The HLR in turn contacts the current serving system and obtains a temporary local directory number (TLDN) from the current VLR. Using the TLDN, the first switch sets up the circuit to the serving MSC.
Typically, there are two types of handoffs in cellular/PCS networks: hard and soft handoffs. During a hard handoff, a mobile prepares a new, better quality link but switches to it only after it drops the air link between itself and its communicating node. During a soft handoff, a mobile can simultaneously have several air links (some of these can be dropped later when they are no longer needed). This phase can last as long as necessary to maintain good quality for the call. Soft handoffs are widely used by CDMA while hard handoffs are widely used by North American TDMA and GSM (also a TDMA system), as well as by AMPS (an FDMA system). Cellular/PCS systems are further described in xe2x80x9cISDN Based C Interface Access for PCS CDMA,xe2x80x9d Special Report SR-3797, Issue 1, Bellcore (December 1995).
While CDPD and Cellular/PCS networks were driven by the need to support wireless end users that may move when they are in a dormant mode as well as in an active (i.e., communicating) mode, mobile IP has a different motivation. It was driven by the need to support end users that would access the network from different points at different times. A mobile IP network consists of mobile nodes, home agents and foreign agents. A home agent is a router that authenticates a mobile node, tracks a mobile""s location, and redirects data packets to the mobile""s current location. A home agent maintains a table of all the mobile nodes that are homed to it with fields such as mobile""s home address and mobile""s care-of-address. A foreign agent assists the mobile node in informing its home agent of its current location, routes data traffic sent by the mobile, and sometimes provides the care-of-address and data packet de-capsulation for the mobile node. A foreign agent also maintains a list of visiting mobile nodes and their information.
Similar to CDPD, mobile IP also uses triangle routing. A mobile""s home agent receives packets destined to the home address of the mobile and tunnels them to the care-of-address of the mobile node by encapsulating the original IP packets in new IP packets with the destination address set to the mobile""s care-of-address. At the care-of address, the original packets are extracted from the tunnel and then delivered to the mobile node. In the reverse direction, packets are sent by the mobile directly to the remote host without tunneling.
Mobile IP with route optimization and smooth handoff is still in the Internet Engineering Task Force (IETF) draft stage, see C.E. Perkins et al., xe2x80x9cRoute Optimization in Mobile IP,xe2x80x9d draft-ietf-mobileip-optim-07.txt (Nov. 20, 1997). A mobile in handoff asks its new foreign agent to send a binding update to its previous foreign agent. During handoff, the previous foreign agent tunnels and the transient packets to the new care-of-address. In case the previous foreign agent has no fresh binding, it can forward the transient packets to the home agent through a special tunnel which prevents routing loops from forming between the home agent and the previous foreign agent. Mobile IP is further described in C. E. Perkins, xe2x80x9cMobile IP,xe2x80x9d IEEE Communications Magazine, pp. 84-99 (May 1997); and J. D. Solomon, xe2x80x9cMobile IP: The Internet Unplugged,xe2x80x9d Prentice Hall (1998). Mobility issues are further described in xe2x80x9cI. F. Akyildiz et al., xe2x80x9cMobility Management in Current and Future Communications Networks,xe2x80x9d IEEE Network, pp. 39-49 (July/August 1998). Also, mobile IP point-to-point communication is described in U.S. Ser. No. 09/150,403, filed on Sep. 9, 1998 (now U.S. Pat. No. 6,496,491 issued on Dec. 12, 2002), and U.S. Ser. No. 09/074,582, filed on May 8,1998, both entitled xe2x80x9cA Mobile Point-to-Point Protocol,xe2x80x9d the disclosures of which are incorporated herein by reference.
However, there are several drawbacks to the individual approaches described above. For instance, as is known, mobile IP networks are typically hampered by route inefficiency problems. On the other hand, as is also known, cellular/PCS networks require significant signaling overhead during call setups and handoffs. As such, there is a need for a network architecture and mobility management techniques that yield an efficient, scaleable, and flexible communications system capable of handling various applications including multimedia applications.
The present invention provides a network architecture, an addressing scheme, and various mobility management methodologies, as well as apparatus for implementing them in a packet-based mobile communications system, which are capable of supporting various voice and data services including, for example, multimedia services.
In a first aspect of the invention, a new protocol layer is provided as part of a protocol stack associated with a packet-based multiaccess mobile communications system. The protocol layer is preferably located above a medium access control (MAC) protocol layer and a physical protocol layer of the system and below a transport/network protocol layer. Such a subnetwork protocol layer provides, inter alia, the communications system with various mobility management functions, for example, tracking mobile user stations throughout the system, mobile station access to the system, and connection/call continuity within the system. The subnetwork protocol layer of the invention also performs packet routing and forwarding functions associated with the system. Routing can be accomplished in many ways, for example, via source routing, connectionless routing, or tunneling. Further, it is to be appreciated that the new protocol layer of the invention is preferably located above a data link layer with respect to the protocol stack associated with communications between network nodes.
In a second aspect of the invention, an addressing scheme for a packet-based multiaccess mobile communications system, which includes a plurality of mobile user stations and a plurality of network nodes, is provided. In such addressing scheme, each mobile station is assigned an address which is a combination (preferably, a concatenation) of a unique identifier of a network node with which the mobile station is currently associated and an identifier of the mobile station. The network node identifiers may be uniquely assigned by a network administrator, while the identifiers of the mobile stations may, for example, be set to a universal MAC address assigned to the station. The address may also include a port identifier which indicates the particular application flow associated with the accompanying packets. Similarly, each network node is assigned an address which is a combination (preferably, a concatenation) of its network node identifier and, preferably, an interface identifier. Since a network node may have links with more than one other network node, the interface identifier uniquely identifies the link with which the packets are associated. The address may also include a port identifier which indicates the particular application flow associated with the accompanying packets. This unique addressing scheme is preferably implemented with respect to the subnetwork protocol layer.
Advantageously, the addressing scheme of the invention alleviates mobile user stations from needing to be concerned with the mobility of other mobile user stations within the system. That is, while the overall address of a mobile station may change due to the fact that it may become associated with a different network node, or a mobile station may have more than one address if it is associated with more than one network node, a correspondent mobile station (e.g., a mobile station with which a first station or initiating station is communicating with or wishes to communicate with) is still able to send and receive packets to and from the initiating mobile station since the identifier of a mobile station (e.g., universal MAC address) remains the same.
In a third aspect of the invention, various methodologies and related apparatus associated with mobility management issues within the system are provided, e.g., location management, mobile access, and in-call mobility management.
Location management techniques according to the invention, for example, include tracking and/or locating mobile stations within the system. The invention makes use of home and visiting location registers in which information such as mobile station addresses, preferably as described above, and/or host names associated with mobile stations are stored. Network nodes may query other network nodes to locate mobile stations based on such databases. Also, mobile stations themselves update such registers to inform them of their current locations. Subsequently, the updated network nodes update other network nodes of such location changes. Network nodes also preferably include a database containing the address for the home location register of each mobile station in the system.
Mobile access methodologies are also provided according to the invention. In one embodiment for use in a mobile station, a complete mobile access method includes searching a database for an address of a second mobile user station, the address being a combination of an identifier of the second mobile user station and an identifier of a network node with which the second mobile user station is currently associated. The first mobile station then transmits a packet containing the address of a second mobile user station and an address of the mobile user station itself, its address being a combination of an identifier of the mobile user station and an identifier of a network node with which the mobile user station is currently associated.
In another embodiment of mobile access according to the invention, a direct mobile access method includes inserting a host name associated with a second mobile user station in a packet, and transmitting the packet to a network node with which the station is in direct communication such that the network node (direct network node) can insert an address of the second station in place of the host name and then transfer the packet on to the second station. The initiating mobile station then preferably receives the address of the second station from the direct network node and replaces the host name with the address in a subsequent packet transmitted to the direct network node. The mobile station may alternatively receive the address of the second station from a home location register of the second station or the second station itself.
The invention also includes various in-call mobility management techniques which make use of the concept of an anchor. An anchor is a network node that is assigned to a mobile user station and acts as a permanent node (i.e., until deleted or changed) to which packets may be intermediately sent. The anchor then passes the packets on to the mobile station, regardless of where the mobile station has moved to in the system. Thus, preferably employing the unique addressing scheme discussed above, packets are directed to an anchor (via, for example, source routing or tunneling) which then directs the packets to the mobile station. If a mobile station moves a sufficient distance from its anchor, the system makes a decision to change the anchor of the mobile station to be a closer network node such as to optimize packet routing. It is to be appreciated that the use of anchors and the addressing scheme of the invention advantageously allow mobile stations to not be concerned with the mobility of another mobile with which it has established an existing connection or call. That is, correspondent mobile stations send packets to anchors which then forward them to the mobile station associated therewith, thus, effectively hiding one mobile station""s location change from another correspondent mobile station.